Tandem with a kidback

Goals

There is a known "problematic period" for a cyclist with kids. At
age from 6 to 11, they are already too big to fit into the rear seat, but not
yet capable of riding along more than several kilometers. This is
described very well at "tandems and kids" page
by Sheldon Brown. When time came, I faced that problem as well. I
started looking for a solution how to cycle with two daughters, who
were 2 and 7 at that moment.

Ready available options

There is not much offer from the industry. Solutions are:

Tandem + kidback

Trailer "half-cycle"

Attaching whole child's bike to the rear of the adult's.

I carefully explored all three options.

Half-cycles

Piccolo half-cycle by Burley

"Piccolo" by Burley were
readily available from Helsinki bike shop Velosport, although the price made me
laugh. I was asked 560€, while in the USA it is available at
average $350, which at that moment made approx. 280€. I
considered ordering a comparable product made by Adams at Harris Cyclery for $160.

But the bad news is that these trailers do not allow riding with two
kids at once. Usually their rod attaches to the seatpost, thus making usage of rear child seat
impossible. Burley's comes with a special rack, the rod mounts to its
center, and this construction is very difficult to modify so that
anything else could be put on the rack. When riding with kids, I
always carry some luggage, and such complete disabling of the rack
seems like an utterly poor design to me.

Add+Bike from
Hoening (later
Roland), a superior and cheaper
product

Later, when my tandem project was almost finished, I
found another trailer called "add+Bike", by that time
from German company hoening.com, in 2010 by
Roland.
It attaches to the very
end of the rear rack (included with the trailer), thus allowing the
second passenger. Their price is competitive, and the rack could be
used as usually! If I had known
about it before, I'd probably not have searched for anything else.
This product is clearly superior to the american competitor, and as
it often happens, loses only on the marketing side.

Connecting child's bike to adult's

Rod, connecting child's cycle to adult's one

These are the "minimal" solution. Available as order items, one is
american-made by www.trail-gator.com, sells for about
$90 in the US, the other is from Germany and could be ordered at many
German bike shops (give a net search for "tandemstange koala")
for about 40 euros.

If they really work, they may beat all other constructions because
the child may ride independently unti exortion, and switch to the
towing mode afterwards. But again they all are fixing to the
seatpost,
which leaves the younger child without a vacant place.

Another way to attach the child's bike

In 2007, I found another German invention:
FollowMe tandem. The pictures
on the site do not show clearly technical details, but this may be
something I'd have liked to try.

Tandem plus kidback attachment

Leaving Hoening's Add+Bike aside, the only remaining option is an
adult tandem. Tandems are fun by itself, although they may be hard to store
in a city apartment. Fortunately our house has a special storage for
bicycles, as most houses in Finland do. Tandems are also expensive,
prices start somewhere at 1500€ plus delivery to Finland. Prices
of local distributives are even much above that, while the selection
is limited by overpriced Cannondales.

But in 2004 the scandinavian supermarket chain Biltema listed in their catalog tandem
for 450 euros. Supermarkets are known for selling bicycles, which are
"not intended to be ridden", but Biltema is doing clear positive steps
in this area every year. I carefully explored that monster and took a
decision to buy it.

Version 1

The next goal was to find the kidback attachment. Until that we were riding
"low-tech" version 1, with a wood stick bound to a frame serving as a
feet prop. It worked somehow, although it should be uncomfortable
to sit on a bicycle saddle not spinning pedals. We made at most 30 km
trips with this setup.

This tandem is just barely acceptable for two full-size adults. I
rode it once with my friend who is also a cyclist, and the Nexus hub
did not break at once, but I was all the time expecting that it suddenly
does.

In fact, most of design decisions of that tandem (not counting
the Nexus hub) are very reasonable:

26" wheels are the only right choice for recreational tandem.
They are stronger compared to the same quality 28" wheels, the frame
accepts wide tires. Also in our case the rear
wheel is dishless because of the
internal-gear hub, thus normal 36-spoke wheel is adequate even for
two adults.

The frame feels quite strong and rigid. Its downtube is
ovalized. In front, there is proper eccentric
bottom bracket.

Both seatposts are standard 27.2mm in
diameter. They were short and old clamp-style, but in front the
length was enough for me with 56cm seat tube, and in the rear
clamp-style seatpost is just what you need to move the child's
saddle about 4cm ahead.

True adjustable stoker stem. For
adult stoker, it was even too long, and I replaced it with
conventional short stem. For a child, it was perfect.

Frame has solid fixtures for the rear rack.

Rims are on the "downhill side" -- good!

Handlebars were 60 and 56cm wide, which is the right choice: the
captain needs wider bar, while the stoker better does not.

The points below make it what I called "barely acceptable"
for a full-strength couple:

1" fork. Well, people used 1" forks on tandems before.

Nexus internal hubs are not approved by Shimano for tandem
usage. Also their important drawback, inability to downshift
under load, hinders even more than on solo bike. To
downshift on an uphill, which is the most frequent and needed case
for a downshift, both riders have to unload pedals simultaneously.

250% of gear range is OK for most circumstances on solo, but is
not enough for a tandem, which rides downhill faster and climbs
uphill slower.

First services

As with most department-store bikes, this one was not properly
adjusted in the store (in fact it was sold in the cardboard box
pre-assembled). I had to do the following small fixes:

Tighten spokes on both wheels. Originally they were terribly
under-tensioned and of course not stress-relieved.

Shifter cable shortened. This
operation is trivial, when you have cable
cutters at hand, and next to impossible otherwise.

Front and rear cranks were actually
not parallel. To syncronize them, a crank
remover was needed.

Plastic pedals replaced so that the
toe clips could be attached.
Later I installed clipless pedals for myself. For a young stoker
toe clips are an important safety feature.

Later, more upgrades/adjustments were done:

Rear saddle replaced with
"grandmother style" one

The rear sprocket was 16 teeth, which
with 42T. chainring in front gave too high
gear ratios for trips with kids. I replaced it with 23T. There is not much
actual power coming from pedaling of a 7 year girl, especially in the
end of the trip, and tandem plus 2 kids weigh 60 kg!

I liked wide handlebar grip for the tandem.
Quick steering is not needed,
but instead fair leverage to control the teal is essential. The stoker
does not reach ground with feet, and the captain must hold the bike firmly.
So I replaced 60cm wide front handlebar with even wider "freeride" bar,
probably 70cm. I am surprised by many pictures of family tandems
with drop bars. In my opinion this is nonsence from any
viewpoint. With kids, you never ride too fast so that aerodynamics is
important, nor too long so that you need different hand positions.
But wide grip and always-at-hand break levers are IMO essential.

Version 2 (with kidback attachment)

View of the complete outcome

Finding the kidback was not an easy task. There are three
"mainstream" american manufacturers,
Burley,
Santana and
DaVinciTandems,
making full kits.
Their products look similarly and the kidback
chain runs on the left side, wrapping over included chainring,
which attaches to the sync chainring. This
would not have worked for me without severe modifications, because
left-side cranks had pressed-in chainrings, and there are no holes to
bolt the second one. Also sync chainrings are 33T -- too small even
to drill these holes in 110mm
BCD.

Another thing I did not like in these kits was an extremely narrow
area where the
kidback fixes to the tandem's seat tube. It is about 4cm wide, and I
was simply afraid that the frame would be bent, although I have not
found reports of such disaster on the net. Burley's version was again in
stock at Velosport for 350€
($180 at Harris Cyclery,
which made less than 150€ at that moment).

Kidback attachment from SJS Cycles

The best unit for my needs is made by British Saint John's Street Cycles, but they
make it only for 28.6mm tubes to fit their own steel tandems and
did not show any enthusiasm to make a custom piece with 31.8mm clamp.
So I was left with
the only possibility to come up with something home-made.

During the summer 2004, one local bike mechanic (let me not name
him) was promising me to weld the kidback. He continued to postpone
the date, until in September he finally said he can not do it at all.
That left us without one summer. I did not expect such kind of
service, which is unfortunately common in Russia, here in
Finland.

Later, I picked a steel frame at a junk field, sawed out the
bottom bracket, and a friend of mine who
has access to metal workshop welded
it to the tube of proper inner diameter. Short cranks were
available in local shops. Originally, I planned to run the kidback
chain to the front right crank, as on Sheldon Brown's
photo. I'll be free from chainline
problems then. But the drawback of this easy setup is that the chain
pulls the bottom bracket not parallel to the seat tube, as in the
mainstream setup, thus applying torsional stress to the tube. I was
uneager to work by trial-and-error with aluminium frame, and in the
end managed with the chain running to the right rear crank. Thanks
planetar gear - that would not work with a front derailer.

The resulting drivetrain

The correct chainline
between the kidback and the rear right chainring was essential now,
and of course required some tweaking. I had to replace the rear
bottom bracket for a shorter one (limited
by clearance between the left sync
chainring and the chainstay -- now
there is about 1mm!).

Clearance between the rear sync chainring and the
chainstay limited the rear bottom bracket length from below

It was not enough, the kidback's
chainring was still much closer to the frame, and I did not
want to increase kidback's Q-factor.
Finally I went by flipping the middle chainring on the old crank, which gave perfect
chainline for both main
chain and sync chain. I must confess
that this successful setup was not the first one I tried.

Right crank with reversed 32T middle chainring

Views of the homemade kidback

First tests showed that the kidback works great. Stoker is proud
of being helpful and feels completely engaged in the ride. The tandem
quickly became favorite transportation means for the children.
When I inform that we are going somewhere by car or bus or train,
kids ask in disappointment: "Why not on tandem?..".

Surprisingly, it turned out that changing to the "adult's" configuration
is very easy. It is enough just to move the rear pedals from the kidback
down to the "unused" rear cranks.
The kidback's cranks are not in the way of the
adult's legs. Of course the kidback with cranks and extra sync chain
can be taken off when not needed, but I was too lazy to do it. Even during
a one week
tandem ride with my wife I just swapped
the pedals, which takes less than 5 minutes.